Liquid crystal display device comprises a liquid crystal cell, polarizing elements, and an optical compensation sheet (a retardation plate). In a transmissive liquid crystal display device, polarizing element is attached to each of two sides of a liquid crystal cell, and between the liquid crystal cell and either one of the polarizing elements, at least one optical compensation sheet is arranged.
A reflective liquid crystal display device is configured generally by arranging a reflector plate, a liquid crystal cell, at least one optical compensation sheet, and a polarizing element in this order. The liquid crystal cell comprises liquid-crystalline molecules, two substrates encapsulating the liquid-crystalline molecules, and electrode layers applying voltage to the liquid-crystalline molecules. For liquid crystal cell, various display modes are proposed depending on variation in orientation state of the liquid-crystalline molecules: TN (twisted nematic), IPS (in-plane switching), FLC (ferroelectric liquid crystal), OCB (optically compensatory bend), STN (supper twisted nematic) and VA (vertically aligned) for a transmissive liquid crystal display device, and HAN (hybrid aligned nematic) for a reflective liquid crystal display device.
The optical compensation sheet has been employed in various liquid crystal display devices in order to cancel coloring of images, and to expand the viewing angle. As an optical compensation sheet, a stretched polymer film was conventionally used. However in recent years, there has been proposed a use of an optical compensation sheet comprising an optically anisotropic layer formed by applying a liquid crystalline composition comprising a liquid crystalline compound to a transparent support in place of the stretched polymer film. As various orientation states can be obtained with liquid crystalline compounds, optical characteristics which have never been obtained by the conventional stretched polymer film can be achieved by using a liquid crystalline compound. Optical compensation sheets for various display modes of a liquid crystal cell using liquid crystalline compounds have been already proposed. For example, Japanese Laid-Open Patent Publication “Tokkaihei” No. 6-214116, U.S. Pat. Nos. 5,583,679 and 5,646,703, and German Patent Application Publication No. 3911620 disclose an optical compensation sheet for a TN mode liquid crystal cell. Japanese Laid-Open Patent Publication “Tokkaihei” No. 10-54982 discloses an optical compensation sheet for IPS and FLC mode liquid crystal cells. U.S. Pat. No. 5,805,253 and WO 96/37804 discloses an optical compensation sheet for OCB and HAN mode liquid crystal cells; Japanese Laid-Open Patent Publication “Tokkaihei” No. 9-26572 discloses an optical compensation sheet for STN mode liquid crystal cell; and Japanese Patent No. 2866372 discloses an optical compensation sheet for VA mode liquid crystal cell.